1. Field of the Invention
This invention relates to a device for digitizing and processing sounds such as melodies and imitation sounds, and particularly to a repetitive PCM data developing device for generating repetitive PCM data used for melody ICs.
2. Description of the Prior Art
The melody IC is different from a tape recorder or the like and is excellent in durability because it does not have mechanical moving parts and in finding the start of music and selecting music. Therefore, it is built in various equipment including a telephone and extensively used as a sound source for background music.
Particularly for melody data, in order to improve sound quality, it is necessary to increase a bit number for analog-digital conversion and sampling frequency. Then, it results in increasing the required memory capacity, decreasing the amount of music which can be stored in the memory. Therefore, it is significant to provide the so-called data compression technology to decrease the required memory capacity without degrading sound quality.
A tone quality of a melody or imitation sound can be generally represented by a systematic waveform such as a sine wave, chopping wave, and square wave. For example, like the original waveform of a melody or imitation sound as shown in FIG. 6A, when the original waveform is a repetition of a similar waveform, by seizing the basic part of the similar waveform as one segment waveform, the original waveform can be closely resembled by repeating the segment waveform as shown in FIG. 6B. A data compression method which has the original waveform closely resembled by repeating the segment waveform is called a repetitive PCM method. And, the repetitive PCM data can be represented by a data form such as (PCM data of segment waveform) x (repetitive number of segment waveform), so that data volume can be substantially decreased as compared with the case that all waveforms are represented by PCM data.
For example, a melody or imitation sound having envelope curve as shown in FIG. 7A will be considered. When the envelope curve representing a tone quality of the melody or imitation sound shown in FIG. 7A is represented by the repetitive PCM method, it can be closely resembled by combining the block data represented by (segment waveform).times.(repetitive number) as shown in FIG. 7B.
To prepare data of a melody or imitation sound by the repetitive PCM method, a block data is prepared by entering information of segment waveform (waveform information, amplitude and frequency) and repetitive number information, and such blocks are combined to finish a final data.
The repetitive PCM method is a method generally used for a melody IC or the like. And, in preparing this type of a melody or imitation sound data, the original sound waveform of a melody or imitation sound is shown on the display, and the waveform information obtained by observing the display is entered in a personal computer and simultaneously it is listened to, and the waveform information is revised to produce the repetitive PCM data which is similar to the original sound.
As described above, in a conventional method, to produce a melody or imitation sound, the original sound waveform of the melody or simulation sound displayed on the CRT is observed to obtain waveform information (segment waveform shape, frequency, amplitude, and repetitive number) and the data is entered to prepare block data, which are combined to produce the repetitive PCM data. But, a recent product adapting a melody IC is required to include various kinds of tone quality within a long-hour melody and imitation data. Therefore, for the analysis of the original sound of a melody or imitation sound, a job for obtaining the waveform information, and a job for combining block data, lots of manpower are required. Thus, it has a problem that many job steps are required.
For example, to prepare data of one musical note, 5 it is necessary to enter waveform information of plural blocks according to similar envelope curves. And to complete the melody of one piece of music, the above steps are conducted on many and various musical notes based on the musical score of the melody. Thus, enormous working volume and working hours are required.